Chapter 22 The Lymphatic System

1. Chapter 22The Lymphatic System • Resistance is the ability to ward off disease • lack of resistance is termed susceptibility • Nonspecific resistance to disease • general defensive mechanisms effective on a wide range of pathogens (disease producing microbes) • Specific resistance or immunity is ability to fight a specific pathogen • cell-mediated immunity • antibody-mediated immunity

2. Lymphatic System • Organs, vessels and a fluid called lymph • similar to interstitial fluid • Organs involved • red bone marrow • thymus • spleen • lymph nodes • diffuse lymphatic tissue • tonsils, adenoids & peyers patches

3. Functions of the Lymphatic System • Draining excess interstitial fluid & plasma proteins from tissue spaces • Transporting dietary lipids & vitamins from GI tract to the blood • Facilitating immune responses • recognize microbes or abnormal cells & responding by killing them directly or secreting antibodies that cause their destruction

4. Lymphatic Vessels & Circulation • Capillaries that begin asclosed-ended tubes foundin spaces between cells • Combine to form lymphaticvessels • resemble veins with thinwalls & more valves • Fluid flows through lymph nodes towards large veins above the heart • lymph emptied into bloodstream

5. Lymphatic Capillaries • Found throughout thebody except in Avasculartissue (cartilage, epidermis& cornea) • Structure is designed to lettissue fluid in but not out • anchoring filaments keep tubefrom collapsing under outside pressure • overlapping endothelial cells open when tissue pressure is high (one-way valve) • In GI tract, known as lacteals -- contain chyle

6. Lymph Trunks & Ducts • Vessels unite to form trunks & thoracic ducts • Right side head, arm & chest empty into right lymphatic duct and rest of body empties into thoracic duct • Lymph is dumped directly into left & right subclavian veins

7. Formation & Flow of Lymph • Fluid & proteins escaping from vascular capillaries is collected by lymphatic capillaries & returned to the blood • Respiratory & muscular pumps promote flow of lymphatic fluid • Lymphatic vessels empty into subclavian veins

8. Lymphatic Organs & Tissues • Widely distributed throughout the body • Primary lymphatic organs • provide environment for stem cells to divide & mature into B and T lymphocytes • red bone marrow gives rise to mature B cells • thymus is site where pre-T cells from red marrow mature • Secondary lymphatic organs & tissues • site where most immune responses occur • lymph nodes, spleen & lymphatic nodules

9. Thymus Gland • Large organ in infants (70 g) but atrophied as adult (3 g) • 2 lobed organ located in mediastinum • Capsule & trabeculae divideit into lobules • Each lobule has cortex &medulla • Cortex • tightly packed lymphocytes &macrophages • Medulla • reticular epithelial cells produces thymic hormones • Hassall’s corpuscles

10. Lymph Nodes • Flow is in one direction • afferent vessels lead in • sinuses lead to efferent vessels that exit at hilus • Only nodes filter lymph

11. Lymph Nodes • Bean-shaped organs, up to 1 inch long, located along lymphatic vessels • scattered throughout body but concentrated near mammary glands, axillae & groin • Stroma is capsule, trabeculae & reticular fibers • Parenchyma is divided into 2 regions: • cortex • lymphatic nodules with germinal centers containing dendritic cells • antigen-presenting cells and macrophages • B cells proliferate into antibody-secreting plasma cells • medulla • contains B cells & plasma cells in medullary cords

12. Metastasis Through Lymphatic System • Characteristic of malignant tumors • Spread of disease from one organ to another • cancer cells travel via blood or lymphatic system • cells establish new tumors where lodge • Secondary tumor sites can be predicted by direction of lymphatic flow from primary site • Cancerous lymph nodes are firm, enlarged and nontender -- infected lymph nodes are not firm and are very tender

13. Spleen • 5 inch organ between stomach & diaphragm • Hilus contains blood & lymphatic vessels • Stroma consists of capsule, trabeculae, fibers & fibroblasts • Parenchyma consists of white pulp and red pulp • white is lymphatic tissue (lymphocytes & macrophages) around branches of splenic artery • red pulp is venous sinuses filled with blood & splenic tissue (splenic cords)

14. Lymphatic Nodules • Concentrations of lymphatic tissue not surrounded by a capsule scattered throughout connective tissue of mucous membranes • mucosa-associated lymphoid tissue (MALT) • Peyer’s patches in the ileum of the small intestine • Appendix • Tonsils form ring at top of throat • adenoids (pharyngeal tonsil) • palatine tonsils (on each side wall) • lingual tonsil in the back of the tongue

15. Developmental Anatomy • Begins to develop by 5thweek • Lymphatic vessels developfrom lymphatic sacs thatarise from veins • Jugular sac & cisterna chyliform thoracic duct • Sacs develop into lymph nodes • Spleen develops in gastric mesentery • Thymus is outgrowth of 3rd pharyngeal pouch

16. Nonspecific Resistance to Disease • Immediate protection against wide variety of pathogens & foreign substances • lacks specific responses to specific invaders • Mechanisms function regardless of type of invader • external mechanical & chemical barriers • internal nonspecific defenses • antimicrobial proteins • natural killer cells & phagocytes • inflammation & fever

17. Skin & Mucous Membranes • Mechanical protection • skin (epidermis) closely packed, keratinized cells • shedding helps remove microbes • mucous membrane secretes viscous mucous • cilia & mucus trap & move microbes toward throat • washing action of tears, urine and saliva • Chemical protection • sebum inhibits growth bacteria & fungus • perspiration lysozymes breakdown bacterial cells • acidic pH of gastric juice and vaginal secretions destroys bacteria

18. Internal Defenses • Antimicrobial proteins discourage microbial growth • interferons • produced by virally infected lymphocytes & macrophages • diffuse to neighboring cells to induce synthesis of antiviral proteins • complement proteins • inactive proteins in blood plasma • when activated enhance immune, allergic & inflammatory reactions • transferrins • iron-binding proteins inhibit bacterial growth by reducing available iron

19. Natural Killer Cells & Phagocytes • NK cells kill a variety of microbes & tumor cells • found in blood, spleen, lymph nodes & red marrow • attack cells displaying abnormal MHC antigens • Phagocytes (neutrophils & macrophages) • ingest microbes or particulate matter • macrophages developed from monocytes • fixed macrophages stand guard in specific tissues • histiocytes in the skin, kupffer cells in the liver, alveolar macrophages in the lungs, microglia in the brain & macrophages in spleen, red marrow & lymph nodes • wandering macrophages in most tissue

20. Phagocytosis • Chemotaxis • attraction to chemicals from damaged tissues, complement proteins, or microbial products • Adherence • attachment to plasma membrane of phagocyte • Ingestion • engulf by pseudopods to form phagosome • Digestion & killing • merge with lysosome containing digestive enzymes & form lethal oxidants • exocytosis residual body

21. Inflammation • Damaged cell initiates • Signs of inflammation • redness • heat • swelling • pain • Function is to trap microbes, toxins or foreign material & begin tissue repair

22. Stages of Inflammation • Vasodilation & increased permeability of vessels • caused by histamine from mast cells, kinins from precursors in the blood, prostaglandins from damaged cells, and leukotrienes from basophils & mast cells • occurs within minutes producing heat, redness & edema • pain can result from injury, pressure from edema or irritation by toxic chemicals from organisms • blood-clotting factors leak into tissues trapping microbes • Phagocyte emigration • within an hour, neutrophils and then monocytes arrive and leave blood stream (emigration) • Tissue repair

23. Abscesses and Ulcers • Pus is dead phagocytes, damaged tissue cells & fluid • Abscess is accumulation of pus in a confined space not open to the outside • pimples & boils • Ulcer is an open sore • People with poor circulation (diabetics with advanced atherosclerosis) • stasis ulcers in tissues of legs due to poor oxygen & nutrient supply to tissues

24. Fever • Abnormally high body temperature that occurs because the hypothalamic thermostat is reset • Occurs during infection & inflammation • bacterial toxins trigger release of fever-causing cytokines such as interleukin-1 • Benefits • intensifies effects of interferons, inhibits bacterial growth, speeds up tissue repair

25. Specific Resistance: Immunity • Immunity is bodies ability to defend itself against specific foreign material or organisms • bacteria, toxins, viruses, cat dander, etc. • Differs from nonspecific defense mechanisms • specificity----recognize self & non-self • memory----2nd encounter produces even more vigorous response • Immune system is cells and tissues that produce the immune response • Immunology is the study of those responses

26. Maturation of T and B Cells • T cell mature in thymus • cell-mediated response • killer cells attack antigens • helper cells costimulate T and B cells • effective against fungi, viruses, parasites, cancer, and tissue transplants • B cells in bone marrow • antibody-mediated response • plasma cells form antibodies • effective against bacteria

27. Antigens • Molecules or bits of foreign material • entire microbes, parts of microbes, bacterial toxins, pollen, transplanted organs, incompatible blood cells • Required characteristics to be considered an antigen • immunogenicity = ability to provoke immune response • reactivity = ability to react to cells or antibodies it caused to be formed • Get past the bodies nonspecific defenses • enter the bloodstream to be deposited in spleen • penetrate the skin & end up in lymph nodes • penetrate mucous membrane & lodge in associated lymphoid tissue

28. Chemical Nature of Antigens/Epitopes • Large, complex molecules, usually proteins • if have simple repeating subunits are not usually antigenic (plastics in joint replacements) • small part of antigen that triggersthe immune response is epitope • antigenic determinant • Hapten is smaller substance thatcan not trigger an immuneresponse unless attached tobody protein • lipid of poison ivy

29. Diversity of Antigen Receptors • Immune system can recognize and respond to a billion different epitopes -- even artificially made molecules • Explanation for great diversity of receptors is genetic recombination of few hundred small gene segments • Each B or T cell has its own unique set of gene segments that codes its unique antigen receptor in the cell membrane

30. Major Histocompatibility Complex Antigens • All our cells have unique surface markers (1000s molecules) • integral membrane proteins called HLA antigens • MHC-I molecules are built into cell membrane of all cells except red blood cells • MHC-II markers seen only on membrane of antigen presenting cells (macrophages, B cells, thymus cells) • Function • if cell is infected with virus MHC-I contain bits of virus marking cell so T cells recognize is problem • if antigen presenting cells (macrophages or B cells) ingest foreign proteins, they will display as part of their MHC-II

31. Histocompatibility Testing • Histocompatibility is a similarity of MHC antigens on body cells of different individuals • tissue typing must be done before any organ transplant • can help identify biological parents

32. Pathways of Antigen Processing • B and T cells must recognize a foreign antigen before beginning their immune response • B cells can bind to antigen in extracellular fluid • T cells can only recognize fragments of antigens that have been processed and presented to them as part of a MHC molecule • Helper T cells “see” antigens if part of MHC-II molecules on surface of antigen presenting cell • Cytotoxic T cells “see” antigens if part of MHC-I molecules on surface of body cells

33. Processing of Exogenous Antigens • Foreign antigen in body fluid is phagocytized by APC • macrophage, B cell, dendritic cell (Langerhans cell in skin) • Antigen is digested and fragments are bound to MHC-II molecules stuck into antigen presenting cell membrane • APC migrates to lymphatic tissue to find T cells

34. Processing of Endogenous Antigens • Endogenous antigens are foreign proteins produced within a body cell --- viral or cancerous • Fragments of weird proteins become part of MHC-I molecules displayed at surface of cell • Signals that a cell need help because it is infected or has turned cancerous

35. Cytokines & Cytokine Therapy • Small protein hormones involved in immune responses • secreted by lymphocytes and antigen presenting cells • Cytokine therapy uses cytokines (interferon) • alpha-interferon used to treat Kaposi’s sarcoma, genital herpes, hepatitis B and C & some leukemias • beta-interferon used to treat multiple sclerosis • interleukin-2 used to treat cancer (side effects)

36. Cell-Mediated Immunity • Begins with activation of T cell by a specific antigen • Result is T cell capable of an immune attack • elimination of the intruder by a direct attack

37. Activation, Proliferation & Differentiation of Cytotoxic T Cells • Receptor on CD8 cell binds to foreign antigen fragment part of MHC-I • Costimulation from helper T cell • prevents accidental immune response • Proliferates & differentiates into population (clone) of Tc cells and memory Tc cells • Occurs in secondary lymphatic organs such as lymph node

38. Activation, Proliferation & Differentiation of Helper T Cells • Receptor on CD4 cell binds to foreign antigen fragment associated with MHC-II • Costimulation with interleukin • Proliferates & differentiates into population (clone) of TH cells and long-lived memory TH cells

39. Types of Mature T Cells • Helper T cells • Cytotoxic (killer) T cells • Memory T cells

40. Helper T Cells • Display CD4 on surface so also known as T4 cells or TH cells • Recognize antigen fragments associated with MHC-II molecules & activated by APCs • Function is to costimulate all other lymphocytes • secrete cytokines (interleukin-2) • autocrine function in that it costimulates itself to proliferate and secrete more interleukin (positive feedback effect causes formation of many more helper T cells)

41. Cytotoxic T Cells • Display CD8 on surface • Known as T8 or Tc or killer T cells • Recognize antigen fragments associated with MHC-I molecules • cells infected with virus • tumor cells • tissue transplants • Costimulation required by cytokine from helper T cell

42. Memory T Cells • T cells from a clone that did not turn into cytotoxic T cells during a cell-mediated response • Available for swift response if a 2nd exposure should occur

43. Elimination of Invaders • Cytotoxic T cells migrate to site of infection or tumor formation • Recognize, attach & attack • secrete granules containing perforin that punch holes in target cell • secrete lymphotoxin that activates enzymes in the target cell causing its DNA to fragment • secrete gamma-interferon to activate phagocytic cells

44. Immunological Surveillance • Cancerous cell displays weird surface antigens (tumor antigens) • Surveillance = immune system finds, recognizes & destroys cells with tumor antigens • done by cytotoxic T cells, macrophages & natural killer cells • most effective in finding tumors caused by viruses • Transplant patients taking immunosuppressive drugs suffer most from viral-induced cancers

45. Graft Rejection • After organ transplant, immune system has both cell-mediated and antibody-mediated immune response = graft rejection • Close match of histocompatibility complex antigens has weaker graft rejection response • immunosuppressive drugs (cyclosporine) • inhibits secretion of interleukin-2 by helper T cells • little effect on B cells so maintains some resistance

46. Antibody-Mediated Immunity • Millions of different B cells that can recognize different antigens and respond • B cells sit still and let antigens be brought to them • stay put in lymph nodes, spleen or peyer’s patches • Once activated, differentiate into plasma cells that secrete antibodies • Antibodies circulate in lymph and blood • combines with epitope on antigen similarly to key fits a specific lock

47. Activation, Proliferation, & Differentiation of B Cells • B cell receptors bind to antigen -- response more intense if on APC • Helper T cell costimulates • Rapid cell division & differentiation occurs • long-lived memory cells • clone of plasma cells • produce antibody at 2000 molecules/sec for 4-5 days • secrete only one kind antibody • Antibody enters the circulation to attack antigen

48. Antibody Structure • Glycoproteins called immunoglobulins • 4 polypeptide chains -- 2 heavy & 2 light chains • hinged midregion lets assume T or Y shape • tips are variable regions -- rest is constant region • 5 different classes based on constant region • IgG, IgA, IgM, IgD and IgE • tips form antigen binding sites

49. Antibody Actions • Neutralization of antigen by blocking effects of toxins or preventing its attachment to body cells • Immobilize bacteria by attacking cilia/flagella • Agglutinate & precipitate antigens by cross-linking them causing clumping & precipitation • Complement activation • Enhancing phagocytosis through precipitation, complement activation or opsonization (coating with special substance)

50. Monoclonal Antibodies • Antibodies against a particular antigen can be harvested from blood • different antibodies will exist for the different epitopes on that antigen • Growing a clone of plasma cells to produce identical antibodies difficult • fused B cells with tumor cells that will grow in culture producing a hybridoma • antibodies produced called monoclonal antibodies • Used clinically for diagnosis -- strep throat, pregnancy, allergies, hepatitis, rabies, cancer